Decades-old cat­alytic con­verter likely re­quires re­moval or re­place­ment

Winnipeg Free Press - Section E - - AUTOS - JIM KERR BACK­YARD ME­CHANIC

QUES­TION: My brother has a 1979 Pon­tiac Parisi­enne with 350,000 kilo­me­tres. It has a 350 cu­bic-inch V-8 en­gine. It has the orig­i­nal cat­alytic con­verter. He was told by a me­chanic and oth­ers that with such high mileage the con­verter can­not be func­tion­ing prop­erly. Is there a way to test this? Would poor gas mileage be a symp­tom? He was told if he re­moves the con­ver­tor and re­places it with a straight pipe the car would not run prop­erly. Is this true and how would it af­fect the per­for­mance? Your opin­ion would be greatly ap­pre­ci­ated. Klaus

An­swer: With mileage that high it is un­likely the cat­alytic con­verter is still work­ing prop­erly. Dur­ing nor­mal use, the cat­alytic con­verter only causes a chem­i­cal re­ac­tion in the ex­haust gases to con­vert them to less-harm­ful gases and does not con­sume it­self, but with that mileage, it has likely be­come con­tam­i­nated so the ex­haust gases can’t come in con­tact with the cat­a­lyst.

It is pos­si­ble to test a cat­alytic con­verter. The best way on older ve­hi­cles such as this one, is to use an ex­haust gas analyzer to see if harm­ful gases are be­ing con­verted. Most shops don’t have ex­haust gas an­a­lyz­ers, but they were used to tune many of the Euro­pean cars in the 1970s and 1980s, so you may find one of th­ese re­pair shops will be able to test it. Since 1996, ve­hi­cles have had an oxy­gen sen­sor be­hind the con­verter so the en­gine com­puter can test the con­verter as part of its di­ag­nos­tic pro­gram.

Poor gas mileage would be a symp­tom if the cat­alytic con­verter is plugged so ex­haust gases can’t flow through it. Many of th­ese ve­hi­cles had the con­vert­ers re­placed with a straight piece of ex­haust pipe and they run fine, but ex­haust emis­sions will be higher. Be­cause there is no mon­i­tor­ing of the con­verter by the en­gine com­put­ers be­fore 1996, there will be no change in en­gine op­er­a­tion.

Ques­tion: Yes­ter­day, the tem­per­a­ture light on my Chrysler Paci­fica came on, so I cut the en­gine off and checked if it needed wa­ter. It was a lit­tle low. Then I’m driv­ing home and my ve­hi­cle kind of jerked for­ward a bit and even­tu­ally died on me. It was smok­ing a lit­tle bit (the coolant was full) so I let it cool down and tried crank­ing it and it turns over but doesn’t catch. My me­chanic sent me a video to­day of what it’s do­ing. There is a lot of smoke com­ing out of the oil filler cap open­ing when the cap is off and if you pull the dip­stick out there is a lot of smoke out the tube too. He thinks I need a new mo­tor. I just need a sec­ond opin­ion. Layne

An­swer: I would have to agree with your me­chanic. The large amount of smoke com­ing from the oil filler and dip­stick in­di­cate too much crank­case pres­sure and the only way for that to hap­pen is if com­bus­tion gases are al­lowed to en­ter the crank­case. The most likely path for this to hap­pen is past the pis­ton rings and with the large amount of “blowby”, as it is usu­ally re­ferred to, I would sus­pect ei­ther sev­eral of the rings are bro­ken or one of the pis­tons has a hole in it.

This could be un­re­lated to the tem­per­a­ture light com­ing on, but if the en­gine has been over­heat­ing, the cylin­der heads can warp and the head gas­kets no longer seal prop­erly. This can al­low coolant into the com­bus­tion cham­ber, which would cause white smoke out of the tailpipe, es­pe­cially when start­ing the en­gine. The coolant can also leak in­ter­nally into the en­gine oil and will dam­age the en­gine bear­ings.

It ap­pears you have se­ri­ous in­ter­nal en­gine prob­lems and the cost of re­pair­ing your ex­ist­ing en­gine is likely much more than re­plac­ing it with a good used one or a fac­tory re­built en­gine.


Over time a cat­alytic con­verter can be­come con­tam­i­nated, pro­hibit­ing the ex­haust gases from con­tact­ing the cat­a­lyst.

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